I wouldn't pay anymore than $250 for it, maybe less depending on condition. I used to have the older model until I came across a newer one for cheap, they work fine but the newer models have a faster pump.
You can always spot the older models by the metal enclosure color, it will be a dull color as opposed to the new ones that use a brushed metal finish, also like you said they have no filter which you really won't notice anyways.